Mecaster duncani ( Fourtau, 1906 ) Mohamed Abdelhamid & Moustafa Azab, 2012

Mohamed Abdelhamid, Marouf Abdel-Aty & Moustafa Azab, Mahmoud, 2012, Turonian-Santonian echinoids from Egypt, Geodiversitas 34 (3), pp. 575-615 : 607-608

Mecaster duncani ( Fourtau, 1906) n. comb. ( Figs 15N; 17F )

Linthia duncani Fourtau, 1906: 162 , pl. 3, figs 1-4.

Periaster duncani – Abdelhamid & El Qot 2001: 29, fig. 7N.

MATERIAL EXAMINED. — 29 specimens from the Turonian (Wata Formation) of Wadi Dakhl, ASUDLE187-215, Wadi Dakhl echinoid horizon 1 ( DEH 1) and 18 from the same stage of Wadi Abu Qaada, ASUAQE170-187, Wadi Abu Qaada echinoid horizon 1 ( QEH 1).

MEASUREMENTS. — See Table 15.

DESCRIPTION

Test polygonal.Maximum width lies slightly behind the distal ends of anterior paired petals. Apical disc semi-ethmolytic, transverse, centric to slightly eccentric anteriorly.Frontal ambulacrum nonpetaloid, and relatively deep.Paired ambulacra deep, wide, and petaloid. Peristome pentagonal, transverse, and labiates. There are two types of fascioles: a wide band of peripetalous ortho- to parafasciole (sensu Néraudeau et al. 1998) and a fine band of lateroanal parafasciole.

R EMARKS

Many authors considered that the post-Cenomanian Mecaster Pomel, 1883 species can develop two fascioles (peripetalous and latero-anal) in fine grained sediments (Lambert 1921; Zaghbib-Turki 1989, 1990; Néraudeau 1994; Villier et al. 2004). Accordingly, many species previously referred to Periaster d’Orbigny, 1853 are attributed to Mecaster (bifasciata ecological varieties of the typical Mecaster species ). The present species has long, sub-equal, moderately depressed paired petals. The apical disc is semi-ethmolytic (madreporite separates genital plates 1and 4). Fascioles are composed of a wide band of peripetalous ortho- to parafasciole sensu Néraudeau et al. (1998) and a narrow band of latero-anal parafasciole sensu Néraudeau et al. (1998; bifasciata stage). The labrum is triangular and long, and the sternal plates are approximately symmetric ( Fig. 17F ). These characters refer this species to genus Mecaster .

Figures

FIG. 17. — Camera lucida drawings: A, phyllode and plastron plating in Toxaster dakhlensis n. sp. from the Turonian of Wadi Dakhl; B, C, Mecaster turonensis (Fourtau,1921) from the Turonian of Wadi Dakhl;B, apical disc;C, phyllode and plastron plating;D, E, Mecaster fourneli (Deshayes,1847) from the Coniacian-Santonian of Wadi Abu Qaada;D, apical disc;E, phyllode and plastron plating;F, phyllode and plastron plating in Mecaster duncani (Fourtau, 1906) n. comb. from the Turonian of Wadi Abu Qaada. Abbreviations: a, first half of the ambulacrum; b, second half of the ambulacrum; f, direction of enlargement of the scrobicules on the sternal plates (indicated by the arrows); V, ambulacrum no. 5. Scale bars: A, C, 2 mm; B, 0.36 mm; D, 0.4 mm; E, 1.4 mm; F, 1.3 mm.